Monitoring Timber Beam Bridges for Structural Health

Abstract

About 2500 timber bridges are on local and regional roads in NSW and many of these bridges were built forty or more years ago. Regular inspections are required to ensure that they have a low probability of structural failure. The aim of this research was to determine if the health of such bridges could be continuously monitored. To test the feasibility of this aim, literature was searched to determine: • The affect that component lifetime has on structure lifetime. • The typical lifetime of a timber component. • How to determine the lifetime of timber components. • The factors that degrade timber beams. • Typical inspection methods and periods as applied to timber bridges. • Current structural measurement techniques for bridges. • Measurement techniques that could be adapted to measure bridge deflection continuously. The performance characteristics of a continuous bridge deflection measurement system was tested for accuracy and calibrated in the laboratory. This measurement system was then applied to a timber beam bridge and the peak deflections caused by normal traffic continuously recorded for a 24 hour period. A method of identifying girder lifetime and structural health is proposed using the deflections produced by light and medium weight traffic, thus precluding the need to proof-load and full-load test timber bridges.